July 16, 2008
In this issue
§ Vegetable insect update
§ Managing tomato diseases
§ Nutrient management following adverse weather
§ Saving nitrogen fertilizer with grass-legume mixtures
§ Regional reports
Next issue July 23
Beth Bishop
Entomology
We are still between flights of European corn borers, but
the second flight will be starting soon in southern
The proportion of aster leafhoppers carrying aster yellows remains moderate. The latest test results from Diagnostic Services indicate that infectivity rate varies among locations, but is generally in the range of less than one percent to eight percent (see table). Because of the variability in infectivity rates, a range of conservative treatment thresholds is suggested.
|
Location and crop |
Date collected |
Infectivity |
Threshold (ALH per 100 sweeps) |
|
|
7 - 7 |
6 percent |
7 to 10 |
|
|
7 - 3 |
0 percent to 3 percent |
12 to 20 |
|
|
7 - 3 |
9 percent |
4 to 6 |
|
(gun swamp) |
7 - 1 |
0 percent |
15 to 25 |
|
Van Buren County, Celery |
7 - 7 |
0 to 2 percent |
15 to 25 |
Squash vine borer moths are flying and searching for places to lay eggs. This day-flying moth can be mistaken for a wasp as it flies through squash fields. Eggs are laid singly at the base of squash plants and the newly-hatched larva eats into the stem at the base. Early in an infestation, the only indications of squash vine borers are piles of sawdust-like frass near entrance holes at the base of squash plants. Later, as the larvae eat the interior of the stem the entire vine wilts and dies.
Squash vine borers can be controlled with two applications of insecticides approximately seven days apart. The first application should be made when moths are flying or signs of larval feeding (frass around entrance holes) are present. Consults bulletin E312: 2008 Insect, Disease, and Nematode Control for Commercial Vegetables for insecticides registered to control squash vine borer on your crop.
Mary Hausbeck and Chandra Howard
Plant Pathology
Bacterial canker is diagnosed yearly in
Once a greenhouse or field is contaminated with bacterial canker, steps must be taken to assure that future crops remain disease free. If a greenhouse is contaminated, remove all plant material from the greenhouse (including weeds and dead plant tissue on the floor), wash and disinfect floor surfaces, hoses, equipment, etc. with a 10 percent solution of bleach or a commercial disinfestant (GreenShield is an example). Wooden structures, such as benches or trays should be soaked in a disinfestant such as bleach (10 percent) or GreenShield for a minimum of an hour and preferably overnight. A simple washing of wooden surfaces is inadequate because of the cracks and crevices that may allow the bacteria to escape a surface wash. Bacteria that overwinter on a wooden surface may be carried to the plants in water droplets next season during the splashing of overhead irrigation.
A contaminated field should be rotated out of tomatoes for at least three years. At one time it was believed that a rotation of at least five years was necessary, however, it is now known that the level of bacteria in a contaminated field drops dramatically after the first year of rotation. Any equipment used in the problem field should be washed and disinfected prior to entering a clean field. Equipment and workers should begin work in the cleanest field and finish with the contaminated field.
Copper sprays every five to seven days may help reduce the spread of bacterial canker. However, if the environment is favorable for bacterial canker (75°F to 90°F with rain) coppers may be limited because the bacteria have a decided advantage in a wet environment.
Avoid working in a diseased field when it is wet to avoid spreading the disease. Bacteria may enter the plant through natural openings, or wounds created by wind, pesticide spraying or insects. A film of water on the leaf surface allows the bacteria to remain viable and move. If workers are moving within a wet field and creating new wounds on the plants, new infections are likely. If plants have been staked, all stakes should be treated as discussed previously for wooden trays and benches.
Bacterial canker is a seedborne disease that has caused
great economic losses for the
Treatments consisted of Kocide 2000 (copper hydroxide) at two lb/A alternated with Kocide 2000 at 1.5 lb/A; OxiDate (hydrogen dioxide) at four pt/A; Tanos (famoxadone and cymoxanil) at 0.5 lb/A alternated with Kocide 2000 at 1.5 lb/A; Actigard (acibenzolar-S-methyl) at rates of 0.02, 0.03, and 0.05 lb/A with remaining applications at 0.05 lb/A alternated with Kocide 2000 at 1.5 lb/A; untreated control. On June 6, treatments were applied preventively and then reapplied every five days through September 2. All treatments received alternating Bravo Weather Stik (chlorothalonil) at 1.5 pt/A and Manzate (mancozeb) at two lb/A applications to prevent fungal infections and were applied at the same time as the bactericidal treatments. All treatments were sprayed from the center of the row outward to encourage natural spread of Cmm from the inoculum source.
On June 7, transplants were inoculated with Cmm and incubated in a greenhouse. On June 9, three inoculated transplants were hand placed adjacent to the first plant in each treatment to serve as a source of inoculum. On June 30, July 21, August 11, and September 2, ten asymptomatic leaflets of approximately the same age and size were randomly selected from the tomato plant at each of the three sample sites that were located zero, nine and 18 feet from the inoculum source.
In our study, Cmm spread 18 feet in three weeks (data not shown). Cmm populations for the Actigard-, Kocide 2000- and Tanos-treated plants were generally lower compared to plants treated with OxiDate or the untreated control, but numbers may not be statistically different. Foliar disease symptoms of OxiDate-treated plants were statistically similar to the untreated control. Actigard and Kocide 2000 offered statistically superior control of bacterial canker foliar symptoms compared with either OxiDate or the untreated control. Tanos alternated with Kocide 2000 effectively suppressed disease symptoms and was shown to be helpful in managing bacterial canker.
|
Treatments |
Leaf incidencez |
Unilateral wiltingy |
Plant vigorx |
|||
|
Untreated control |
30.00 |
aw |
69.75 |
a |
5.00 |
a |
|
OxiDate |
40.00 |
a |
72.75 |
a |
4.00 |
a |
|
Kocide 2000 |
10.00 |
bc |
40.25 |
b |
7.25 |
bc |
|
Tanos alternate Kocide 2000 |
21.25 |
b |
18.25 |
ab |
6.00 |
b |
|
Actigard alternate Kocide 2000 |
7.50 |
c |
18.25 |
b |
8.00 |
c |
z Percent of leaf exhibiting marginal leaf necrosis.
y The number of strikes exhibiting unilateral wilting over a 22.5 foot treatment row.
x Overall plant vigor was rated on a one to 10 scale, with 10 being a completely disease free plant, 8: showing less than 10 percent marginal necrosis or minor unilateral wilting; 6: increased marginal leaf necrosis but less than 30 percent or moderate unilateral wilting; 4: increased marginal leaf necrosis but less than 50 percent or severe unilateral wilting; 2: increased marginal leaf necrosis but less than 70 percent or entire plant showing unilateral wilting symptoms; and 1: dead plant.
w Different lower case letters within the same column denote statistical difference (p < 0.05).
Late blight is a fungal disease that most commonly affects
potatoes, but can affect tomatoes in some years. When the weather is favorable,
late blight can be a very serious disease. Although this disease was not a
reported problem in
Between cropping seasons, the fungus survives on volunteer and abandoned potato and tomato plants in fields, cull piles, and homeowner gardens. Cool nights and warm days are ideal for late blight development. The spores can be carried from diseased plants to nearby healthy plants via wind.
Control measures include eliminating all potato cull piles in the vicinity of tomato plantings and destroying volunteer potato plants that grow from overwintered tubers. All tomato varieties are susceptible to late blight. When late blight on potatoes has been reported in the state, fungicides that control late blight are recommended for tomatoes.
Anthracnose is caused by the fungus Colletotrichum coccodes and causes a rotting of ripe fruit which reduces yield and fruit quality. Disease symptoms do not appear on the foliage. Early symptoms include slightly depressed, water-soaked circular spots that increase in size (up to a half inch), become further sunken and may contain a pattern of concentric rings. As the fungus spreads within the fruit, a semi-soft decay occurs. Lesion development is most rapid at 80°F and disease development is greatest during wet, rainy weather. To control the disease, a two- or three-year crop rotation is suggested. Also, avoidance of sandy soil sites to minimize injury from blowing sand particles will reduce anthracnose.
Early blight is caused by the fungus Alternaria solani and infects foliage and ripening fruit. Infection can occur at the point of attachment to the stem and through growth cracks and wounds on the fruit. The early blight fungus causes dark brown, leathery sunken spots with concentric rings. When young fruits become infected, they may drop off prematurely. Infection is greatest in warm weather (75°F to 85°F). Heavy dews, extremely humid weather and abundant rainfall are essential for heavy disease pressure. To control the disease, a three- or four-year rotation will reduce the levels of the fungus in the soil.
Soil-rot is caused by the fungus Rhizoctonia solani and causes slightly sunken brown spots about one inch in diameter on fruit that are in contact with the ground. Dark concentric markings are distinct within new spots and eventually the center of the spot may crack. Disease usually appears on ripe fruit in contact with soil. Disease is promoted by wet conditions. The pathogen is present in all field soil and affects tomato fruit whenever conditions are favorable.
Darryl Warncke
Crop and Soil Sciences
Many vegetable fields have received excess rain and other adverse weather conditions. Loss of nitrogen by leaching or denitrification is a primary concern. Being able to dry the soil and till it to get oxygen back into the soil improves microbial activity and the mineralization of nitrogen. In order to further deal with these situations, sidedress 25 - 50 lbs N/acre. For onions, apply no more than 25 lbs N/acre. More at this time could delay maturity and storage quality. For later planted vegetable crops with a high nitrogen requirement apply 40 - 50 lbs N/acre.
Boron may also be leached out of the root zone under excess water conditions. For boron responsive crops, spray the foliage with 0.25 lbs B/ acre. Boron responsive crops include the root crops, celery, celeriac, broccoli, cauliflower and tomato. Chinese cabbage and pak choi are less responsive, but may also benefit from a boron spray.
Many of the vine crops, leafy green crops, radish and sweet corn will benefit from spraying the foliage with manganese at 1 lb Mn/acre.
Under stress conditions plants may benefit from spraying some other nutrients as well, but stressed plants are less able to absorb nutrients through their leaves. For more information on nutrient management, check out MSU Extension bulletins E-486 and E-2934.
Daniel Brainard
Horticulture
As nitrogen fertilizer costs increase, the potential benefits of using legume cover crops to supply nitrogen is becoming more economically attractive. However, legumes tend to be less effective at suppressing weeds and have relatively high seed costs compared to other cover crops. Mixtures of legumes with grasses can help overcome these problems, and provide additional benefits compared to legumes grown alone.
Mixtures have several potential advantages relative to legumes grown alone:
§ Mixtures of legumes can reduce seed costs by allowing substitution of high-cost legume seeds with lower cost grasses. Legume seeding rates can often be reduced by about 50 percent in mixtures with grasses.
§ Mixtures are often better at suppressing weeds than monocultures of legumes alone. Legumes tend to be slower growing and less capable of smothering weeds than non-legume counterparts. Complementary grass cover crops can serve as nurse crops for legume establishment and take up space and resources that might otherwise be occupied by weeds.
§ Mixtures reduce risks associated with pure stands of either cover crop; if pests or environmental stresses restrict growth of one species, the other can often fill the gap. Similarly, variation in soil moisture or soil nutrients across fields will result in less variation in cover crop growth when two or more complementary species are included in the mix.
§ Legumes in mixture can be more efficient at fixing nitrogen, since the non-legume draws down soil nitrogen, resulting in stimulation of legume nodulation and nitrogen fixation. For example, in our studies comparing cowpea grown alone with cowpea grown in combination with Japanese millet, more nitrogen was fixed per plant in the mixture, resulting in lower costs per pound of nitrogen fixed.
§ Grass and legume mixtures provide a residue with a balanced C:N ratio for which the timing of nitrogen release is better matched to crop demand. In contrast, nitrogen from residues of pure stands of legumes like hairy vetch is often quickly mineralized and lost before crops can use it, while high C non-legume residues like rye can tie-up nitrogen and suppress early crop growth.
The most serious problem with legume-grass mixtures is the potential suppression of the more valuable and costly legume by the non-legume. For example, in experiments evaluating sorghum-sudangrass in combination with either soybean or cowpea, sorghum-sudangrass suppressed both legumes, resulting in poor nitrogen-fixation. In this case, pure stands of either crop would be preferable. Similarly, aggressive cover crops like buckwheat do not usually do well in mixtures with legumes. Rapid canopy closure by buckwheat cover crops suppresses early legume growth. Buckwheat also needs to be mowed about 40 days after seeding to avoid seed production. This combination of shading and mowing leaves little opportunity for most legumes to fix nitrogen. Fields with high soil nitrogen fertility are also poor candidates for legume-grass mixtures. High soil nitrogen tends to favor non-legumes in mixtures and suppress nitrogen-fixation resulting in poor legume stands. Temperature can also have a strong impact on legumes grown in mixture. For example, cool temperatures tend to favor rye in rye-vetch mixtures, so planting mixtures of these species late in the fall can result in dominance of rye at the expense of vetch.
For mid-summer cover crop plantings, cowpeas (Red Ripper or Iron Clay) have performed well in combination with summer grasses including pearl millet, German millet and Japanese millet (Photo 1). Oats and peas are a proven combination for early spring or late summer plantings. In late summer, they can produce substantial biomass and nitrogen before winter-kill, leaving a manageable residue in the spring (Photo 2). Winter rye and hairy vetch are a reliable combination for fall plantings (Photo 3). In addition to the benefits described above, this combination is thought to improve overwinter survival of vetch, and reduce harmful allelopathic effects of rye on subsequent crops. Several new early flowering, winter-hardy hairy vetch varieties developed at USDA Beltsville, including ‘Purple Bounty’ and ‘Purple Prosperity’ are being tested for compatibility with winter rye, and may expand the already strong potential of this combination for vegetable growers. However, hairy vetch can become a formidable weed problem in perennial crops like asparagus or winter grains, so it should be avoided on farms with either of these crops in their rotation.
Ron Goldy
Temperatures have been near to slightly below normal for the period with lows from 60°F to 66°F and highs from 76°F to 88°F. There was 0.50 to 1.50 inches of rain across the area.
Sweet corn is being harvested. Some plantings have high numbers of Japanese beetles feeding on the leaves. Growers should be concerned about the second generation of European corn borer and corn earworm.
Tomatoes are being harvested from early planted, tunneled fields.
Zucchini, yellow squash and cucumber harvest volume has increased due to more fields coming into production. Some early fields are close to being abandoned. Growers should remove these plantings as soon as possible after last harvest so they don’t serve as reservoirs for disease and insect problems.
Watermelon, cantaloupe, pumpkin and fall squash growth has increased due to favorable temperatures and rainfall. Squash vine borers are active, so growers need to take control steps.
Colorado potato beetle continues to be a problem on eggplant.
Peppers are growing well and setting fruit.
Tarnished plant bugs are still active.
There will be an open house for the high tunnel system July 31 from 7:00 to 9:00 PM.
Bill Steenwyk
Most areas in counties surrounding
Crop report
Celery is looking better and growing rapidly after taking weeks of too much water. In some fields where the hearts rotted, new growth is underway. The early harvest in some locations is decreased and overall maturity in earlier transplanted fields is delayed.
Onions, like celery, are a mixed story. Although flooding damaged some fields, growth is recovering. Bulb diameter is approaching two inches in some fields.
Several leek fields were damaged by past heavy rains.
Radish growth and harvest continues. The second crop appears to be doing well.
The first sweet corn is nearly ready for harvest. I've noted some occasional nitrogen deficiency by the typical, yellow streaking down the midrib, starting at the tip of the older leaves, as shown in the accompanying photos. If growers see the same in younger corn, additional nitrogen is needed. Pheromone trap counts were zero European corn borer moths and two corn earworm moths.
Cabbage growth and harvest is moving along well. Quality in many fields is good, despite some rain-related losses on low and steeply sloping fields.
Development of tomatoes and peppers is good overall.
Squash and other cucurbits are growing rapidly, although
some fields were damaged by excess water. I have heard reports of phytopthora
spreading in some zucchini fields. I
have not seen or heard of additional downy mildew, besides the reports last
week in
Norm Myers
In asparagus, new fern growth is coming along fine. Wet conditions and warmer temperatures are increasing danger of foliar diseases like stemphyllium purple spot and rust. Most growers will put a fungicide down as soon as the fern is fully developed.
For carrots, foliar diseases are a big concern in this crop. Many growers are treating for bacterial blight on a weekly basis and TOM-Cast is calling for a spray for fungal blights.
Zucchini and pumpkin growers are already putting on fungicide for powdery mildew and pickle growers are generally following Dr. Hausbeck’s recommendation for downy mildew. Cucumber beetle control has also been a challenge, but growers finally seem to have a handle on it.
Summer snap bean plantings appear to be growing normally in most areas.
The very earliest plantings of sweet corn are now in tassel and silk. My European corn borer traps had no moths, but I did have two corn earworms. I also had 14 western bean cutworms in one of my traps for last week and another 14 the following morning. I will begin scouting that field for egg masses next week.
Jim Breinling
Temperatures and rainfall in the area were consistent during the past seven days. Temperatures were unseasonably cool over the weekend following the rainfall and subsequent cold front on Saturday, July 12. Rainfall received in the area was uniform with 0.66-inch and 0.65-inch respectively at the Fremont and Ludington Enviro-weather stations.
In general, growth and development in all vegetable crops was good this past week, and insect pressures remained about the same.
Low numbers in the European corn borer traps continue at the
Trap counts at the
Sudeep Mathew
We had dry weather with some widespread rains during the
past week. There is some water damage in pepper, potatoes and cucumber fields.
According to the Enviro-weather
station in
Sweet corn harvest is moving into full swing this week. In some of the late planted sweet corn fields, thrips feeding is evident on fully emerged leaves. It was interesting to see that the thrips population was only noticed at this particular growth stage of sweet corn. Our European corn borer traps didn’t find any moths this past week. However, I did find one corn earworm moth in the corn earworm trap.
Peppers are maturing well. Preliminary rounds of harvesting are going on in fields.
Green beans are in high demand and the crop is in excellent condition.
Cucumbers, melons, cantaloupes, pumpkins and squash are maturing. The first few rounds of picking are progressing in cucumber fields. Cucumber downy mildew is spreading (Photo 1). I have seen symptoms in a few more fields this week. Home gardeners also started to bring samples to our office. Let me remind everyone how important it is to follow the spray schedule recommended by Dr. Mary Hausbeck to minimize yield impact.
Squash vine borer was found in a pumpkin field (Photo 2). There were four squash vine borers found in our trap.
Cauliflower is being planted in fields where sweet corn has been harvested.
Cabbage packing and wholesale sales are gaining momentum. Area growers are busy with the shipping of harvested crops. I was at a growers harvesting site this week and it was impressive to see the excellent quality of cabbage and cauliflower from the region.
Greenhouse grown and field market tomatoes are being harvested. Processing tomatoes are making good growth. Vines are maturing and the fruits are setting a good quality fruit (Photo 3).
Potatoes are also looking good. Canopy closure and tuber bulking is forming at a fast pace. Very few leafhoppers were found in many potato fields. I have found 10 variegated cutworm moths in our trap.